1. Field of the Invention
This invention relates to vacuum operable switches. More specifically the switches are utilized for automobile transmissions, which switches may include snap action discs operable between two distinct positions in response to a pressure differential.
2. Description of the Prior Art
Snap-action switches of various configurations are known and illustrated in the prior art. Various spring and diaphragm arrangements as well as disc operators, have been disclosed for use in pressure-operable switches.
Pressure operable are clearly illustrated by U.S. Pat. Nos. 4,330,695--Poling; 4,328,406--Evans et al; and, 4,145,588--Orcutt. These patents disclose a snap-action disc operator responsive to a fluid pressure to engage and close a switch. In all three patent disclosures, the fluid pressure acts directly on the disc surface to move the switch actuating means.
U.S. Pat. No. 3,867,594--Graf et al illustrates a flexible diaphragm operated stem to deflect a dish-shaped conductor to close a circuit. Alternatively, U.S. Pat. No. 3,816,685--Fiore discloses a pressure operable disc diaphragm utilizing a free-moving stem to close a switch.
Vacuum-operated switches are shown in U.S. Pat. Nos. 4,334,131--Cooper et al and 4,272,660--Mayer et al. In the '131--Cooper et al patent, a rubber piston is spring-biased to maintain contact between two contact wipers and a set of terminals. This device is not a snap-action switch but relies on closing separate circuits at different times with the contact points.
The '660--Mayer et al patent discloses a metal diaphragm that is responsive to a vacuum. The switch includes normally-open and normally-closed poles, and a snap action arrangement changes the switch position therebetween.
The above-noted art describes various pressure activated structures, but the paucity of vacuum-activated switches is indicative of the lack of development in such switches. Pressure-activated devices are a significant factor in the art especially for snap-action switches utilizing resilient metallic, bimetallic or combination metallic-nonmetallic members. The utilization of a rapidly-responsive, pliable diaphragm in cooperation with a metallic resilient device to actuate a snap action function in a switch assures an improved seal to protect the switch means while providing a predetermined hysteresis function of a predictable resilient operator.